A rather tame ltxnsp wasrecently found on Easter Island by a retired neurophysiologist. Hereported the following measurements of ECF and ICF concentrations(in millimoles):

ICF ECF
Pr+ 0 150
Na+ 100 10
K+ 10 100
Cl- 109 250
HCO3- 1 10

He determined that the rising phase of the action potential in ltxnsp neurons was due to a sudden increase in PK. What should be the sign and approximate amplitude of the voltage change of these action potentials? Why?